Vibrating sensors, such as for example, vibrating densitometers and Coriolis flow meters are generally known and are used to measure mass flow and other information for materials within a conduit. The material may be flowing or stationary. Exemplary Coriolis flow meters are disclosed in U.S. Pat. No. 4,109,524, U.S. Pat. No. 4,491,025, and Re. 31,450 all to J. E. Smith et al. These flow meters have one or more conduits of straight or curved configuration. Each conduit configuration in a Coriolis mass flow meter has a set of natural vibration modes, which may be of simple bending, torsional, or coupled type. Each conduit can be driven to oscillate at a preferred mode.
Material flows into the flow meter from a connected pipeline on the inlet side of the flow meter, is directed through the conduit(s), and exits the flow meter through the outlet side of the flow meter. The natural vibration modes of the vibrating, material filled system are defined in part by the combined mass of the conduits and the material flowing within the conduits.
When there is no flow through the flow meter, a driving force applied to the conduit(s) causes all points along the conduit(s) to oscillate with identical phase or a small “zero offset”, which is a time delay measured at zero flow. As material begins to flow through the flow meter, Coriolis forces cause each point along the conduit(s) to have a different phase. For example, the phase at the inlet end of the flow meter lags the phase at the centralized driver position, while the phase at the outlet leads the phase at the centralized driver position. Pick-off sensors on the conduit(s) produce sinusoidal signals representative of the motion of the conduit(s). Signals output from the pick-off sensors are processed to determine the time delay between the pick-off sensors. The time delay between the two or more pick-off sensors is proportional to the mass flow rate of material flowing through the conduit(s).
Meter electronics connected to the driver generates a drive signal to operate the driver and determines a mass flow rate and other properties of a material from signals received from the pick-off sensors. The driver may comprise one of many well-known arrangements; however, a magnet and an opposing drive coil have received great success in the vibrating meter industry. Examples of suitable drive coil and magnet arrangements are provided in U.S. Pat. No. 7,287,438 as well as U.S. Pat. No. 7,628,083, which are both assigned on their face to Micro Motion, Inc. and are hereby incorporated by reference. An alternating current is passed to the drive coil for vibrating the conduit(s) at a desired flow tube amplitude and frequency. It is also known in the art to provide the pick-off sensors as a magnet and coil arrangement very similar to the driver arrangement. However, while the driver receives a current, which induces a motion, the pick-off sensors can use the motion provided by the driver to induce a voltage. The magnitude of the time delay measured by the pick-off sensors is very small; often measured in nanoseconds. Therefore, it is necessary to have the transducer output be very accurate.
FIG. 1 illustrates an example of a prior art vibrating sensor assembly 5 in the form of a Coriolis flow meter comprising a flow meter 10 and a meter electronics 20. The meter electronics 20 is connected to the flow meter 10 to measure characteristics of a flowing material, such as, for example, density, mass flow rate, volume flow rate, totalized mass flow, temperature, and other information.
The flow meter 10 includes a pair of flanges 101 and 101′, manifolds 102 and 102′, and conduits 103A and 103B. Manifolds 102, 102′ are affixed to opposing ends of the conduits 103A, 103B. Flanges 101 and 101′ of the prior art Coriolis flow meter are affixed to opposite ends of the spacer 106. The spacer 106 maintains the spacing between manifolds 102, 102′ to prevent undesired vibrations in the conduits 103A and 103B. The conduits 103A and 103B extend outwardly from the manifolds in an essentially parallel fashion. When the flow meter 10 is inserted into a pipeline system (not shown) which carries the flowing material, the material enters flow meter 10 through flange 101, passes through the inlet manifold 102 where the total amount of material is directed to enter conduits 103A and 103B, flows through the conduits 103A and 103B and back into the outlet manifold 102′ where it exits the flow meter 10 through the flange 101′.
The prior art flow meter 10 includes a driver 104. The driver 104 is affixed to conduits 103A and 103B in a position where the driver 104 can vibrate the conduits 103A, 103B in the drive mode, for example. More particularly, the driver 104 includes a first driver component (not shown) affixed to the conduit 103A and a second driver component (not shown) affixed to the conduit 103B. The driver 104 may comprise one of many well-known arrangements such as a coil mounted to the conduit 103A and an opposing magnet mounted to the conduit 103B.
In the present example of the prior art Coriolis flow meter, the drive mode is the first out of phase bending mode and the conduits 103A, 103B are selected and appropriately mounted to inlet manifold 102 and outlet manifold 102′ so as to provide a balanced system having substantially the same mass distribution, moments of inertia, and elastic modules about bending axes W-W and W′-W′, respectively. In the present example, where the drive mode is the first out of phase bending mode, the conduits 103A and 103B are driven by the driver 104 in opposite directions about their respective bending axes W-W and W′-W′. A drive signal in the form of an alternating current can be provided by the meter electronics 20, such as for example via pathway 110, and passed through the coil to cause both conduits 103A, 103B to oscillate. Those of ordinary skill in the art will appreciate that other drive modes may be used by the prior art Coriolis flow meter.
The flow meter 10 shown includes a pair of pick-offs 105, 105′ that are affixed to the conduits 103A, 103B. More particularly, a first pick-off component (not shown) is located on the conduits 103A and a second pick-off component (not shown) is located on the conduit 103B. In the example depicted, the pick-offs 105, 105′ may be electromagnetic detectors, for example, pick-off magnets and pick-off coils that produce pick-off signals that represent the velocity and position of the conduits 103A, 103B. For example, the pick-offs 105, 105′ may supply pick-off signals to the meter electronics 20 via pathways 111, 111′. Those of ordinary skill in the art will appreciate that the motion of the conduits 103A, 103B is proportional to certain characteristics of the flowing material, for example, the mass flow rate and the density of the material flowing through the conduits 103A, 103B.
In the example shown in FIG. 1, the meter electronics 20 receives the pick-off signals from the pick-offs 105, 105′. Path 26 provides an input and an output means that allows one or more meter electronics 20 to interface with an operator. The meter electronics 20 measures a characteristic of the flowing material, such as, for example, a phase difference, a frequency, a time delay, a density, a mass flow rate, a volume flow rate, a totalized mass flow, a temperature, a meter verification, and other information. More particularly, the meter electronics 20 receives one or more signals, for example, from the pick-offs 105, 105′ and one or more temperature sensors 130.
Due to the relatively small phase delay as well as the extremely accurate measurements achievable by Coriolis flow meters, the temperature of at least one of the flow conduits is typically measured using a temperature-measuring device, such as a resistance temperature detector (RTD) 130. Unless the process material's temperature is rapidly changing, the temperature of the flow conduit is related to the process material's temperature and is proportional to the thermal impedance between the fluid, the RTD, and the ambient temperature. Therefore, if the temperature of the conduit can be measured, the temperature of the fluid can be determined to within an accepted degree of certainty, which may depend upon the particular application. Therefore, prior art vibrating meters, such as the prior art Coriolis flow meter 10 utilize a well-known RTD 130 to generate a temperature measurement of the flow conduit. In some prior art systems, multiple measurements are taken with multiple RTDs to obtain temperature measurements of the conduit, a case surrounding the conduits, brace bars, etc.
RTDs are widely accepted as providing an accurate temperature measurement. A RTD operates by applying power to the RTD and calculating the resistance of the RTD. This is typically done by supplying a known current through the RTD and measuring the resulting voltage to calculate the resistance. The RTD's resistance is directly proportional to temperature. For example, many RTDs are made from platinum that has a relatively linear temperature coefficient of resistance of approximately 0.00391° C. Therefore, the RTD can be calibrated to provide a temperature based on a determined resistance of the RTD. RTDs have the advantage of being accurate, stable, fairly linear, and have a wide temperature range. However, one of the main disadvantages of using a RTD is the increased cost associated with operation of the RTD. The increased cost is a result of the cost of the RTD itself as well as the signal processing of the low signal levels typical of RTDs. While the increased cost associated with RTDs can be justified in some situations, other situations do not require the constant temperature measurement or the high accuracy provided by an RTD. One such example is in situations where the temperature of the process fluid remains relatively stable. A RTD may not be required in this situation because the anticipated temperature range is relatively limited and temperature influences are reduced compared to density or volume measurements.
Therefore, there exists a need in the art to provide a temperature measurement of at least one of the conduits of a vibrating meter using an existing sensor component. Namely, there exists a need to provide a temperature measurement without requiring an extra component, such as the RTD 130 of the prior art Coriolis flow meter 10. The present invention overcomes these and other problems and an advance in the art is achieved.